SEC Lite Descriptors
MPC885 PowerQUICC Family Reference Manual, Rev. 2
49-6
Freescale Semiconductor
49.3
Descriptor Chaining
Following the length/pointer pairs is the ‘Next Descriptor’ field, which contains the pointer to the next
descriptor in memory. Upon completion of processing of the current descriptor, this value, if non-zero, is
used to request a burst read of the next-data-packet descriptor. This automatic load of the next descriptor
is referred to as descriptor chaining.
Figure 49-6
displays the next descriptor pointer field.
Table 49-7
describes the descriptor pointer field mapping.
Descriptor chaining provides a measure of ‘decoupling’ between host CPU activities and the status of the
SEC Lite. Rather than waiting for the SEC Lite to signal DONE, and arbitrating for the bus in order to
write directly to the next-data-packet descriptor in the crypto-channel, the host can simply create new
descriptors in memory, and chain them to descriptors which have not yet been fetched by the SEC Lite by
filling the next-data-packet field with the address of the newly created descriptor. Whether or not
processing continues automatically following next-descriptor fetch and whether or not an interrupt is
generated depends on the programming of the Crypto-Channel’s Configuration Register.
Table 49-6. Descriptor Length/Pointer Mapping
Descriptor
Type
L/P 1
L/P 2
L/P 3
L/P 4
L/P 5
L/P 6
L/P 7
0000
nil
IV
Key
Data In
Data Out
IV Out
MAC Out
0001
nil
IV
Key
Data In
Data Out
IV Out
MAC Out
0010
HMAC Key
HMAC Data
Key
IV
Data In
Data Out
HMAC/Context Out
0011
MD Ctx In
IV
Key
Data In
Data Out
IV Out
MD/Context Out
0100
nil
IV
Key
Data In
Data Out
IV Out
Key Out via FIFO
1100
HMAC Key
HMAC Data
Sym
Key
Sym Context
Data In
Data Out
HMAC/Context Out
1101
MD Ctx In
IV
Key
Data In
Data Out
IV Out
MD/Context Out
0
31
Field
NEXT DESCRIPTOR POINTER
Reset
0
R/W
R/W
Figure 49-6.
Next
Descriptor Pointer Field
Table 49-7. Descriptor Pointer Field Mapping
Bits
Name
Reset Value
Description
0–31
NEXT
DESCRIPTOR
POINTER
0
The Next Descriptor Pointer Field contains the address, in global memory
space, of the next descriptor to be fetched if descriptor chaining is enabled.
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